Mercury and acid gas emission control is desired by the power generation industry. A more facile way of controlling mercury and acid gas emissions from heat generating systems is sought by the industry.
An established methodology currently in practice for the control of mercury emissions is the addition of halogen containing compounds to fuels or to flue gases to enhance the oxidation of mercury, thereby facilitating its capture by sorbents and scrubber liquors (see U.S. Pat. No. 6,808,692 and U.S. Pat. No. 6,878,358, both of which are herein incorporated by reference). However, the current use of activated carbon-type compounds for mercury adsorption can adversely affect the potential sale of fly ash products by the power generation industry, resulting in a desire for an inorganic sorbent capable of mercury adsorption without affecting fly ash quality.
Current emission control strategies for acidic gas species (e.g., HCl, SO2, and SO3) rely on solid sorbents for removal of pollutants from exhaust gas streams. The reduction of HCl, SO2, and SO3 are achieved by injection of basic sorbents into a dry scrubber or upstream of particulate control devices (e.g., electrostatic precipitator, fabric filter, or Venturi seperator). In particular, basic materials are injected into the flue gas stream to contact the gas and neutralize acid gases, including hydrogen halides, SO2, SO3, and other acid gas species. Typical sorbents include hydrated lime (i.e., Ca(OH)2), sodium carbonate (i.e., Na2CO3), sodium bicarbonate (i.e., NaHCO3), and trona (i.e., Na2CO3.NaHCO3.xH2O). Although sodium-containing sorbents can be effective, they are often prohibitively expensive owing to localized availability and their propensity to foul power plant equipment. Additionally, sodium-containing sorbents are often soluble in water, and can potentially leach into the surrounding environment after the ash is landfilled. On the other hand, hydrated lime is relatively inexpensive; however the reactions between acid gases and hydrated lime are often less efficient than with their sodium-containing counterparts. Accordingly, there exists a need for improved sorbents for control of mercury and acidic gas species emissions from gas streams.